Shock Wave Propagation Through a Series of Perforated Plates

Abstract

A simplified analysis can be employed to predict the pressure buildup behind a porous barrier fairly accurately without resorting to numerical modeling. A macroscopic approach is used in which the pressure buildup behind the porous barrier is analyzed in relation to the load inflicted on its front face thus allowing finding the effects of the different parameters of the porous barrier. This method was successfully employed to study the impingement of shock waves and blast waves on stiff silicon carbide foams and more recently on buildings that had enough internal divisions as to be considered as a low porosity medium. In this study, the methodology is employed to study a porous barrier comprised from an array of perforated plates with various porosities to determine the parameters affecting the pressure buildup behind it. Perforated plates were chosen since the geometry of the barriers assembled from the plates is simple enough so it can be exactly defined, and still the shock structure and the developing fields are so complicated that only few studies attempted to deal with similar scenarios in the past. In fact, previous studies were limited to one or two perforated plates. In the experiments presented, 3 mm plates were placed 8 mm apart inside a 32 mm by 32 mm shock tube. The last plate was mounted 10 mm from the end wall. The plates were drilled to accommodate various blockage ratios (defined as blocked to open area ratio) ranging from 50% to 80%. It was found that the volume of air confined inside the porous medium undergoes an adiabatic process, and thus the pressure buildup time at the end wall depends on the volume to the power of the heat capacities ratio.